Unloader for compressors



Patented Feb. 26, 1952 UNITED STATES PAT EN T OFFICE UNIJOADER FOR COMPRESSORS James ;H. Anderson, Easton, Pa., assignor :to *Ingersoll-Rand Company, New York, -N. Y., a

corporation of New Jersey Application May28, 1948, Serial No. 29,707 3 Claims. (omen-=27) :1 T hisinventionrelates:tooompressors, and more ---'particularly "to an unloader for afcompressor "driven ibyua constant V- -speed driver, such as a synchronous electric :motor, which is not readily ;-;adapted ;for ::varying -;:the capacity :of '-;the comreaches a particular point on its-suction stroke, -in other words, by varying the spring pressure n": the valve, it is allowed .toclose at correspond- ;ingly varying positionsof the piston during the (,Other objects Will-be in-part obvious and in part-pointed out hereinafter.

vInithe accompanying drawings in-which similar reference numerals refer to similar; parts,

1: Figure 1 ;-is a top view, partly broken away, 5 of a :iportion of a I compressor; embodying one ;form ofthe present invention, and

Figure 2 is an enlarged-view, partly broken away, of the discharge valve mechanismshown in'Figureil.

Referring more particularly to the drawings and at first :to Figure ilk-apportion of a compressor designated, in general by 20, is shown as having a casing 2| forming a compression chamber 22 within whichis a reciprocatory piston 23 for compressing-the'fiuid -medium. Acylinder head 24 covers the end of the-compression chamber "22 and has'an inlet port 25 anda discharge-port 26ifor'thecompression chamber located adjacent thereto.

Air is conveyed by an t. intake line 29 to 1 an inlet chamber. 21. inthe head 24, whenceit passes through :theinlet port 2 5 into the compression chamberf22. .The flow of air through the port .25 isicontrolled .by -a typical compressor inlet valve 28. The aircompressedinthe compression chamber 22 passes through the port 26 into a clearance chamber 30 in the cylinder head 24 and is conveyed therefrom by a discharge conduit 3| which, in this instance, is provided with a flap-type check valve 32 for checking the rushof the housing '45 by bolts .58. nectedinto the chamber 52 is a pipe 53 which conveysa fluid whosepressure may be varied back or" compressed air into the clearancechamhorde-from a receiver Knotshown) To control communication between --the compression chamber .22 and the clearance chamber 39 and to serve the additional function of unloading the compressor, a valve mechanism 33 is adapted to be :held firmly seated in the discharge port 26 by adjustable push rods 34 threadedly connected into a head plate The valve mechanism33 selected for the purpose-of illustrating a practical application of the invention is ofthe type forming the subject matter of the Baker patent forCompressor Valve-No. 2,112,875, granted April -5, 1938. Accordingly the valve mechanism :33 comprises ;a body 36 having a plurality of ports '3! and a cover 38 having ports I 9 therein through which all of the air from the compression chamber is discharged.

Channel valves 33 positioned between the body 36 and cover 38 and adapted to control the :flow

of compressed fluid through the ports 3! and I9 are normally held seated over the ports 31 by arcuate shaped springs 40 acting between the valves 39 and members 4| on the .cover 38. Each channel valve '39 has the usual side flanges 42 which, in this case, have apertures for receiving the :hooked open ends of a-U-shaped hanger 43 which is connected at the mid-point of its arcuate portion tolan arm 44 of a liftermember 45.

Situated adjacent :the clearance chamber 30 and in line with the valve mechanism 33 is a tubular housing :46 which is attached to the cylinder hea'd 24 by bolts- 41-and is partitioned by a'member to form :a cup-shaped opening in the outer end of the housing to receive a piston 48. The piston 48 is provided with a stem :49

which eXtendsthroug-h an aperture in the partition' 50 into a chamber 54 definedbythat portion of "the housing {closest to the clearance chamber 30. An abutment 5i on the stem 49 is designed to constantly maintaina chamber 52 between the piston'48 and the partition 53.

The piston 48 is constantlyurged toward the partition-50 by a spring .56 acting between "the piston-and a plate 51 secured over ,the open end However, conto -.the chamber 5Z2 from an outside source (not shown) for moving thepistoni lfi away from the partitioni5fl a distant:e-correspondin-g.tothepressure of said fluid. Communication between @the chamber 52 and chamber 54 which opens directly into the clearance chamber 30 is prevented by a seal 55 in the partition 50 surrounding the piston stem 49.

In order to permit rapid motion of the channel valves 39, a coil spring 59 extends through an opening in the head plate 35 and forms a connecting member between the cross bar 45 and the piston stem 49. The spring '59 has its ends projecting through apertures in the opposed ends of the member 45 and stem 99 and is further adapted to transmit any tension which may be exerted on the piston 48 by the pressure fluid in the chamber 52, through the cross bar 45 to the valves 39.

In normal operation, the air compressed in the compression chamber 22 on the compression stroke of the piston 23 urges the valves 39 from their seats and passes through the valve mecha- 'nism 33 into the clearance chamber 39, from whence it travels into the discharge conduit 3! through the check valve 32 and on into a receiver (not shown). In such operation the valves 39 have a certain closed period during each piston cycle. However, when the occasion arises where less compressed air output is required from the compressor, a fluid having a selected pressure is fed into the chamber 52 through the pipe 53 by any suitable-means (not shown), thus moving the piston 48 from its seated position against the partition 59. This consequently exerts a tension on the spring 59 which is transmitted through the cross bar hanger arrangement to the valves 39 and will overcome some of the pressure exerted on the valves 39 by the springs 49 which normally hold the valves seated during all of the suction stroke of the piston 23.

Now the force tending to hold the valves seated is considerably less than that normally exerted by the springs 49 and the piston 23 must move over a portion of its suction stroke before the pressure difierential between the clearance chamber 39 and the compression chamber 22 is great enough to overcome the tension holding the valves 39 open. The closed period-of the valve is thereby shortened during this type of operation. However, the air compressed in the compression chamber 22 will still pass into the clearance chamber 39, but a portion of that air will be allowed to travel back into the compression chamber during part of the suction stroke of the piston 23 thereby partially unloading the compressor.

It will be noted that by introducing a very high pressure fluid into the chamber 52 the valves 39 may be held unseated at all times, thereby unloading the compressor completely. By varying the pressure of the fluid in the chamber 52 then, the degree of unloading is likewise varied, since the valves 39 may be caused to operate during each piston cycle at times corresponding to varying positions of the piston 23 on the suction stroke.

It will be further understood that the spring 59 not only allows the free movement of the valves 39 each piston cycle but also transmits a certain tension from the piston 98 which tends to overcome the pressure of the springs 49 on the valves 39. Moreover, this tension does overcome the pressure of the springs 49 during portions of the suction stroke of the piston when partial unloading of the compressor is desired. With the present invention then, infinite degrees of compressor unloading may be attained and selective control of said unloading is made possible. Also, since the degree of unloading may be varied between successive piston cycles it is possible to maintain a practically constant discharge pressure regardless of the load on the compressor.

It will be apparent to those familiar with the art to which this invention appertains that various modifications and changes may be made without departing from the spirit of the invention or the scope of the claims.

I claim:

1. In an unloader for a compressor, a casing having a compression chamber, a reciprocative piston therein, a clearance chamber, a valve for controlling communication between the compression chamber and the clearance chamber, a spring normally exerting pressure on the valve, a housing adjacent the clearance chamber and forming a chamber, a pressure fluid operated piston in said chamber, and resilient means connecting the last said piston to the valve to allow the piston to partially relieve the spring pressure on the valve to vary the closed period of the valve during the suction stroke of the piston.-

2. In an unloader for a compressor, a casing having a compression chamber, a reciprocative piston therein, a clearance chamber, a discharge valve for controlling communication between the compression chamber and the clerance chamber, a spring normally acting to seat the valve, a housing adjacent the clearance chamber and forming a chamber, a piston in said chamber, a stem for the piston, a spring attached to the stem and to said valve, and means for introducing a variable pressure fluid into said chamber to actuate said piston and partially relieve the pressure of the first-mentioned spring on the valve to vary the closed period of the valve during the suction stroke of the piston.

3. In an unloader for a compressor, a casing having a compression chamber, a reciprocative piston therein, a clearance chamber, a discharge valve for controlling communication between the compression chamber and the clearance chamher, a spring normally acting to seat the valve,

a lifter member attached to said valve, a housing adjacent the clearance chamber and forming a chamber, a piston in said chamber, a stem for the piston, a spring connected between the stem and lifter member, and means for introducing a variable pressure fluid into said chamher to actuate said piston and vary the closed period of the valve.

JAMES H. ANDERSON.

REFERENGES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 831,522 Reardon Sept. 18, 1906 1,138,199 Donaldson May 4, 1915 1,579,782 Riesner Apr. 6, 1926 1,587,015 Longacre June 1, 1926 1,621,913 Longacre Mar. 22, 1927 2,112,875 Baker Apr. 5, 1938 2,241,195 Gehres May 6, 1941 2,346,987 Newton Apr. 18, 1944 FOREIGN PATENTS Number Country Date 688,429 Germany 1938 

